1. Technical Field
This invention relates generally to Short Message Service operations in mobile cellular telecommunication networks. More particularly, this invention relates to a method to provide Short Message Service (SMS) services to mobile units roaming in a Signaling System #7 (SS7) network different from the Mobile Station (MS) home network.
2. History of Related Art
The Short Message Service (SMS) provides a means of sending text messages, containing up to 160 alphanumeric characters, to and from mobile stations. SMS makes use of a Message Center (MC), which acts as a store and forward center for short messages. The performance of different telecommunication network entities during an SMS operation is described in the American National Standards Institute (ANSI)-41 telecommunications standard, including the SMS Delivery Point to Point (DPTP) operation. This operation is defined as “a general purpose operation that is used to convey a short message or in general any other information or encapsulated data from one point to another point and report on the success or failure of that transfer.”
When a MS registers at a Mobile Switching Center-Visitor Location Register (MSC-VLR), the MSC-VLR sends a Registration Notification Invoke (REGNOT) message to the Home Location Register (HLR). This message contains the address of the MSC currently serving the MS. This information is used by the HLR to find the MS. The MSC-VLR may provide the following ANSI-41 parameters in the REGNOT message: Point Code-Subsystem Number (PC-SSN), MSCIdentification (MSCID), MSCIdentificationNumber (MSCIN), and the SMS Address. Additionally, the Signaling Connection Control Part (SCCP) address information, such as Point Code or Global Title Address (GTA), may be used by the HLR to locate the MS.
When a Short Message Entity (SME) receives a request to deliver an SMS, the SME sends the SMSDPTP Invoke message to the MC. When the destination of the Short Message is a MS, the MC requests the address of the serving MSC from the HLR. This may be accomplished using an ANSI-41 SMS Request Invoke (SMSREQ) message. Since the HLR already has the information regarding the MS location, it will respond to the SMSREQ message with the serving MSC Address. The address of the serving MSC (SMSC) is provided to the MC in the SMS Request Return Result (smsreq) in the ANSI-41 parameter “SMS Address.”
This SMS Address may be the SMS Address parameter received in response to the REGNOT message, or the PC SSN, or the MSCID translated into a PC SSN, or even the lower layer SCCP information received during registration. With such information, the MC is able to send the SMS to the MSC, and the MSC forwards it to the MS via air interface, (typically TDMA or CDMA). The HLR can also provide the MS's Serving MSC Address using a SMS Notification (SMSNOT) message. This message is used when the MS is inactive at the time the HLR receives a SMSREQ message.
The preferred way to provide the SMS Address in the smsreq message is for the HLR to use the same SMS Address parameter received at REGNOT. Currently, the use of alternate addresses such as the MSCID, the PC-SSN, or the MSCIN to provide the SMS Address has disadvantages. For example, using the MSCID received during registration requires translation to a point code by the HLR, so its use may not be recommended. Using the PC-SSN parameter, or the lower layer address, may point to the VLR instead of the MSC when the MSC and VLR are different entities, thus creating confusion. Finally, the MSCIN parameter is not currently used by the HLR for SMS purposes, and is mainly used to let the HLR know that the MSC is International Roaming capable.
The SMS Address parameter has been modified in various usage standards, and it is suggested to use an E.212 address (taken from the International Telecommunication Union (ITU) Recommendation E.212 “International Identification Plan for Mobile Terminals and Mobile Users”, incorporated herein by reference in its entirety) for international SMS message routing, and either an SS7 point code address or an E.212 address for national scenarios. When the MSC determines that the MS is roaming into a different SS7 network, the MSC may include its own E.212 address number in the SMS Address parameter in the REGNOT message. In this case, the HLR will populate the same SMS Address in the smsreq response message. This method is efficient for an international scenario, that is, when the MSC and MC are not connected by a common national signaling point code addressing scheme (i.e., utilize a different SS7 network type).
However, to provide SMS services to a national MS roaming in a different SS7 network, the MSC is required to provide the SMS Address with a Global Title Address (GTA) during registration, i.e., an E.212 GTA or E.164 (the ITU Recommendation E.164 “The International Public Telecommunication Numbering Plan”, incorporated herein by reference in its entirety) GTA identifier, or a combination of these two identifiers. When a national roaming MS registers with the MSC, the MSC will typically provide a PC address in the SMS Address parameter in the REGNOT message (or the smsreq response). The HLR will store this address and provide it when a MC requests the address. However, a problem with this scenario occurs if the MC that issues the SMSREQ is in a different SS7 network type than the HLR (and therefore the S-MSC). The smsreq response from the HLR will include a PC in the SMS address provided by the MSC that is not recognized by the MC as the intended SMS address. Therefore, the SMSDPTP operation will not be possible.
Therefore, what is needed is a method which allows the HLR to determine the proper address for the MSC (or VLR) serving the roaming MS when requested by an external node. This method should enable communication between the external node and the MS, MSC, or VLR, so as to provide proper addressing of SMS services to MSs roaming in an SS7 network that is different from the MS home network, and SMS reception from SS7 networks not being used by the MS.